Launch managers at Cape Canaveral Air Force Station in Florida scrubbed the launch of NASA's Radiation Belt Storm Probes early this morning, just four minutes before takeoff.
The United Launch Alliance Atlas V carrying NASA's Radiation Belt Storm Probes (RBSP) had been due to lift off at around 4.00 am EDT this morning.
But a problem with the rocket's Eastern Range tracking beacon has delayed things by 24 hours, while engineers attempt to work out whether the problem's with the beacon itself or with ground equipment.
The next launch attempt is scheduled for tomorrow, August 25, at 4.07 am EDT. Like today, the launch window will extend for 20 minutes.
It's the second delay for the RBSP launch, after a potential fault with the engine was discovered during testing of another Atlas vehicle at the factory in Decatur, Alabama. Engineers had to make sure the same condition didn't exist on the RBSP launch vehicle.
The RBSP mission is to study the Van Allen radiation belts, which consist of radioactive particles trapped by the Earth's magnetic field. The inner ring extends out to about 4,000 miles above Earth, while the outer ring reaches from 8,000 miles to about 26,000 miles from Earth.
It's hoped that the twin probes will reveal more data about how different particles move around the Earth, improving space weather forecasts.